Naphtha air sweetening



April 12, 1960 G. w. OSTBERG 2,932,313

V NAPI-ITHA AIR SWEETENING Filed June 15, 1955 2 Sheets-Sheet 1 FIGUREI0 FIGURE Ib FIGURE JI George W. Ostberg Inventor By Attorney April 2,1960 G. w. QSTBERG 2,932,318

NAPHTHA AIR SWEETENING Filed June 13, 1955 2 Sheets-Sheet 2 INHIBITORAIR I STORLkGE SETTLER, MIXER TAN I lz l} I6 I4 20 MIXER '2 SPENT ICAUSTIC I cAusTIc I 28 SOUR FIGURE I NAPHTHA NAPHTHA TANK -20 :36 7 a iI I I AL; I a -II-I 34 FIGURE 111.

FIGURE JI George W Qsfberg Inventor WW 7Attorney United States PatentNAPHTHA AIR SWEETENING George W. Ostberg, Roselle Park, NJ., assignor toEsso Research and Engineering Company, a corporation of DelawareApplication June 13, 1955, Serial No. 514,993

8 Claims. (Cl. 137-592) The present invention relates-to a process andapparatus for sweetening naphtha compositions. More spe oifically, inaccordance with the present invention sour gasoline stocks are sweetenedby contact with air in a storage tank equipped with baffling meanswhereby maximum residence time of control between incoming air andnaphtha is realized to produce a completely air sweetened naphtha. Y I

The removal of undesired sulfur compounds from petroleum products is aperennial problem in the petroleum refining industry. While there havebeen many suggestions made as to processes for removing undesired sulfurcompounds, the desire for simplified sulfur removal processes remains.Again new problems are encountered in the processing of novel feedstocks or unusual blends of stocks.

comparatively recently it has been discovered that certain stocks aresusceptible to what is known as air sweetening. For example, certaingasolines during simple storage under conditions to expose the gasolinesto oxygen will undergo a process in which mercaptans are converted todisulfides. This conversion of sulfur compounds from mercaptans todisulfides is called sweetening by virtue of the fact that thedisulfides, unlike the mercaptans, are not malodorous. The basicsimplicity of the air sweetening process holds great promise as afinishing procedure for stocks susceptible to this treatment in order toprovide the last incremental improvement in sweetening which is oftenrequired. The present invention is concerned with animprovcment in airsweetening techniques providing for increased rates of sweetening ofthose stocks which respond to air sweetening. It is a particular featureof the process that it has been found to be of particular application tothe sweetening of blends of cracked gasolines with virgin gasolines,since virgin gasolines are normally unresponsive to air sweetening.

1 In commercialinstallations, sour naphtha is generally sweetened instorage tanks under conditions to obtain thenecessary residence time toconvert mercaptans to disulfides. This residence time, of the order of24 to 96 hours, depending upon the characteristics of the crude, hasbeen obtained by passing air-treated naphtha from amixingzone to astorage tank equipped with two inlet nozzles. One nozzle is located atground level and the second about 10 feet above the lower nozzle. Whenthe tank is empty or nearly so, the lower inlet nozzle is usedfor'filling. The naphtha is passed in at production rate, i.e., the,rate at which it is produced at the processing unit. When the naphthalevel reaches the upper nozzle, the lower connection is shut off and theupper one is opened. This allows. the incoming naphtha, which is usuallywarmer than the naphtha in tankage, to remain as'the top stratumof thenaphtha. Since the naphtha is withdrawn through a nozzle or port, alsosituated at ground level, the naphtha that is withdrawn from the bottomis that which has remained in the tank for the longest period. Thearrangement described has been found not to be completely satisfactory.In the first place, it requires 2,9323% Patented Apr. 12, 1960 2constant operating attention to insure proper closure and opening ofvalves, depending upon the level of the airtreated naphtha within thetank. Also, there is a potential safety hazard of naphtha dischargingthrough the elevated nozzle above the liquid level of the naphtha.Furthermore, when the level of'the naphtha is appr e; ciably above thetopinozzle, maximum residence time is not attained as the horizontallyentering naphtha mixes and circulates with naphtha partially aged inthe'tanks.

It is, therefore, the principal object of the present invention to setforth a naphtha sweetening tank specifically adapted to overcome theabove mentioned disadvantages in commercial installations.

It is a further purpose and object of the present invention to set fortha tank arrangement aifording a maximum of residence time, elimination ofoperating attention, and elimination of a potential safety hazard.

Other and further objects and advantages of the present invention willbecome apparent hereinafter.

In accordance with the present invention the second or upper nozzle ofthe tank is replaced by a suitable bafile such as a plate or box bafllc.The bafile is installed with sufficient clearance from the tank. floorso that with normal flow input, the level within the bafiled section isabout 3 to 6 inches higher than the level on the storage side. Thebafiie extends upward for approximately one third to one half of theheight of the tank. When the naphtha level in tankage reaches the top ofthe baflle -l00% of the flow is upward, and the remainder is through theunderclearance to the bottom portion of the tank. This division isaffected by both the warmer temperature of the incoming naphtha and thehigher resistance to flow underneath the bafiie. Consequently, theincoming naphtha is diverted vertically to the top of the naphthavolume, and maximum residence time for the sweetening and aging isobtained.

The present invention will be more clearly understood when read inconjunction with the drawings which represent schematically preferredembodiments thereof.

In the drawings:

Figure I is a schematic diagram of a process for sweetening sournaphtha.

Figure Ia is a partial top sectional view of naphtha storage tank 20 ofFigure I.

Figure Ib is a partial top sectional view of a modification of thestorage tank shown in Figure la.

Figure II is a partial side sectional view of a naphtha storage tankwherein the bafile is pipe 30.

Figure III is a plan view of the storage tank in Figure II with theinterior baffie shown in dotted lines.

Figure IV is a partial side sectional view of a modification of thestorage tank shown in Figures II wd III.

Turning now to Figure I, the sour naphtha is preferably given apreliminary caustic wash in vessel 2 to remove hydrogen sulfide, whichwould be converted to free sulfur in the subsequent air treating step.The naphthas to be sweetened by this process may be identified byreference to the mercaptan content of the stock. As indicated by thecopper number of the gasoline, the sweetening process is particularlyapplicable to those gasolines, having a copper number ranging from about1 or less, to 15. As will be understood, such gasolines may alsoconstitute gasolines obtained from prior sweetening operations or fromrelatively low sulfur crude oils, and particularly from gasolinesderived from thermal or catalytic cracking operations.

Caustic soda employed for the caustic wash may be introduced throughline 4 for mixture with the sour naphtha in vessel 2, which may be anorifice mixer. About 1-10 volumes of 530% caustic may be employed.

It has also been found desirable to add an antioxidant inhibitor to thenaphtha prior to or during the subsequent air-sweetening process. Ofparticular effectiveness are the phenylene diamines, inparticular, theN,N" .di-alkyl- The caustic-washed naphtha is then passed to an air'-'mixing zone 16. Air may be introduced throughlin'e, 18

by means of a compressed air line'or 'the 'lik'e'; The air injectedshould not be less than about 0.05 standard cubic foot per copper numberper barrel ofnaph'tha treated; Thus for a gasoline of 10 copper number,0.5's.c.f. of

air per barrelis about the minimum requirement, but

about 1.5 s.c.f. is preferred to speed up the sweetening rate.

The process is preferably operated continuously, but throughput must becontrolled so that the hold-up time in zone 26 is sutficient to completesweetening.

In accordance with the present invention, the naphtha admixed with airis conducted to bathed storage'vessel 20. This vessel is-a conventionalstorage tank adapted for storing volatile and inflammable hydrocarbonsbut, in accordance with the present invention, also equipped with bathe22. The vessel is of sufficient size for 4 days production hold-up, forexample 40' diameter by 36' height. Battle 22 may be of plate (FigureTa) or box (Figure lb) design and its lower portion afiords a clearanceor underpass of about 5 to square inches, that is,

the bathe is installed with sutficient clearance from the tank floor sothat with normal flow input of 1600-4000 barrels per stream day, thelevel within the bafile section is' 3-6 inches higher than the level onthe storage side. The bafile extends upwardly approximately one half theheight of the tank. In one embodiment, it is welded to the tank wall.

The air-mixed naphtha is passed into tank through line 24 and nozzle 26.As indicated previously, initially the level within the bathed sectionis some 3-6 inches higher than the level on the storage side, thenaphtha passing under the bafile. At this stage, it is generally notdesirable to withdraw naphtha from outlet nozzle 28, due to incompleteageing. When the naphtha level in the tankage reaches the top of bathe22, 95-100% of the flow is upward and the remainder through theunderclearance in the bottom portion of the tank. This results in partfrom the warmer temperature of the incoming naphtha which may be 70 to100 F. while the bottom portion approaches ambient temperature, say 50'to 80 F., and also by the higher resistance to flow underneath thebattle. Thus the incoming naphtha is diverted vertically to the top ofthe naphtha volume and the maximum residence time for ageing isobtained. The tank may be filled to a level substantially above the topof the bathe without loss of effective residence time.

After a holdmp period of 24 to 96 hours, the aged product, now fullyair-sweetened, is withdrawn from tanks 20 through outlet nozzle 28 andis further processed in a manner not forming a part of the presentinvention. Thus, it may be water-washed if desired, or passed directlyto storage. Similarly, tank 20 may be further provided with vents andoutlets towithdraw air separated from the naphtha.

Though the process and construction of the present invention find theirimmediate utility in the air sweetening of naphtha, it is evident thatthey find utility inother applications where a maximum of residence timeof a liquid in a tank, for aging 'or' other effect, is desired. Theadvantages of the present invention over present installations andprocesses include the elimination of operating attention to the tank inthat there are no valves to openor close, depending upon the' levelwithin'the' tank; the elimination of the -potential safety hazard ofnaphtha discharging through an elevated nozzle above the liquid level ofthe naphtha; and the full effectiveness of the baffie installation atall levels above the top of the battle. In prior arrangements, maximumresidence time could not be realized when the naphtha level wasappreciably above the top nozzle.

Another embodiment of the present invention is shown in .Eigure Ii. Thebafiling effect is provided by a vertical pipe 30 coupled to the tankinlet nozzle 32. Pipe 30 is about 10-20 feet in length and 12-16 inchesin diameter, and the corresponding nozzle may be 4-6 inches in diameter.Opposite the inlet nozzle in pipe30 is slot 34, having an area of 5-10square inches, providing for bottom flow of naphtha into the tank, as inthe case of the battle previously described. If desired, a swingor othertype check valve maybe, used instead of bottom slot or orifice 34. Sucharrangement is shown in Figure IV.

In a typical tank employing this alternate pipe 30 may be installed in anaphtha storage tank 40 feet in diameter and 36 feet high. Standpipe 30is 12 inches in diameter and stands 15- feet high. Slot 34 measures 1inch by 5 inches, and the'diilerential bead through slot 34 is about 4inches. The naphtha flows upwardly through standpipe 30 and passes-intothe tank through. its upper openings 36. The relationship of standpipe30' to tank 20 is clearly seen inFigure III.

T he standpipe arrangement has the advantage of minimizing welding inthe tank, cheaper and simpler construction, and easier installation. The12" pipe with a 4" connection may readily be carried into a tank of? say40 diameter and '36 height through the standard 24" manhole. The largersize standpipe, say 16" size with 6" connection is used for larger tankshandling large naphtha rates, and can be entered through the standard28" manhead on these tanks.

What is claimed is:

1. 'In a naphtha storage tank in combination. a tank, conduit inletmeans in the lower portion of said. tank adapted to conduct vaporizableliquids into said tank, a' vertical bathe attached to the side wall ofsaid tank to form a flow space between said bafile and said side wallwhich communicates with said inlet means, said bafile being positionedabove the floor. of said tank and extending upwardly to /2 the height ofsaid tank, said baffle additionally being positioned close to saidinlet. means and extending. downwardly to form with the floor of saidtank an opening having substantially smaller cross" section than saidinlet means, and conduit means in the lower portion of said tank adaptedto withdraw said liquid, said last named conduit means being furtherremoved from said bathe than said conduit inlet means.

2. The apparatus of claim 1 wherein said battle is a plate baffle.

3. The apparatus of claim 1 wherein said baflle is a box baffle.

4. The apparatus of claim 1' wherein said inlet means is a nozzle.

5. In a naphtha storage tank in combination a tank, conduit inlet meansin the lower portion of said tank adapted to conduct vaporizable,liquids, a vertical pipe positioned on the floor of said tank and incommunication with said inlet means, said pipe extending for a distanceof about /s- /z the height of said tank and the upper portion of saidpipe being in open communication with said tank, outlet means in thelower portion of said pipe, said outlet means being of substantiallysmaller cross section than said inlet means, and conduit means in thelower portion of said tank adapted to withdraw said liquid, saidlast-named means being substantially further removed from said pipe thansaid inlet means,

6. The apparatus of claim 5 wherein said outlet means from said pipe issubstantially opposite said inlet means.

References Cited in the file of patent UNITED STATES PATENTS 357,793Smith Feb. 15, 1887 1,212,574 Shipp Jan. 16, 1917 1,635,414

Hirst July 12, 1927 6 Schnetzler Oct. 28, 1930 Waechter Nov. 23, 1937Poirier July 6, 1948 Temperly May 6, 1952 Davies Mar. 10, 1953 MackinnonFeb. 15, 1955v FOREIGN PATENTS Great Britain Aug. 22, 1907 Great BritainSept. 21, 1907

